1. Field of the Invention
This invention relates to a motor drive system and, more particularly, to an electric motor drive system suitable for driving precision machines and so forth.
2. Description of the Related Art
Many a drive system incorporating an electric motor have been used in precision machines such as cameras, in which the motor and a speed reducing mechanism are often combined together into one drive unit and installed in the system to facilitate assembling operation.
To gain higher driving speeds of a motor drive system using such a drive unit, installation of a newly designed drive unit and changes in motor characteristics of the drive unit already designed are contemplated, that is, through a first method of replacing the motor with a low-impedance motor to thereby increase motor output, through a second method of replacing the motor with a larger-size motor in order to provide a greater starting torque and to decrease the reduction ratio of a reduction gear, and through a third method of adopting a core-less motor.
The first method, however, has a drawback that a motor speed increases excessively high, resulting in deteriorated durability if motor impedance is set too low. According to the second method, utilization of a large-sized motor and change of the reduction mechanism are required. And moreover it is impossible to utilize a designed drive unit and it is difficult to improve the whole driving speed range from starting to stopping because of lowered starting and braking characteristics of the motor. Furthermore, according to the third method, the driving speed of the motor in a steady state makes no difference from that of conventional motors despite an increase in transient driving speeds resulting from improved motor starting and braking characteristics, thereby raising the price of the motor and accordingly the cost of commodities using the motor drive system.